High frequency coil



Sept. 22, 1942. N. M. RUST 2,296,452

HIGH FREQUENCY COIL Original Filed April 24, 1956 INVENTOR ATTORNEY Patented Sept. 22, 1942 HIGH FREQUENCY COIL Nol Meyer Rust, Chelmsford, England, assignor to Radio Corporation America, a corporation of Delaware Original application April 24, 1936, Serial No. this application September 76,122. Divided and 4, 1940, Serial No. May 11, 1935 use in electrical high irequency circuits and to circuit arrangements incorporating the same.

355,301. In Great Britain This application is a division of my copending application S. N. 76,122, filed April 24, 1936, which has matured into Patent No. 2,227,846 on January 7, 1941.

An important object of the invention is to provide improved quarter wave and half wave length coil constructions which shall be very cheap, light, and of low losses and which can be made directly self-supporting, i. e., without needing terminals or mountings. Where terminals or mountings are provided they are arranged to be out of the field oi. the coil.

According to this invention, a coil structure for use as a resonant device in high frequency electricalcircuit arrangements comprises an inner conductive coil winding positioned within an outer conductive screen member and is characterized in that said winding and screen member are so constructed and supported that there is no solid dielectric material between the face of said winding presented to said screen member and said screen member.

The invention is illustrated in the accompanying drawing, in which:

Fig. l is a longitudinal section of an improved coil construction oi this invention;

Fig. 2 is a cross-section of Fig. 1;

Fig. 3 is an elevation 01 another construction of coil structure with part of the screen portion broken away to show its construction;

Fig. 4 is an end view of Fig. 3;

Fig. 5 is a developed view of part of the screen conductor;

Fig. 6 is a perspective view of another modification of screen structure to be substituted for the screen structure shown in Figs. 3, 4 and 5; and

Fig. '1 is an end view of Fig. 6.

Referring to Figs. 1 and 2 which are mututally perpendicular sectional views showing one form of construction in accordance with the invention, a quarter or hall wave length coil construction comprises a helix l of solid conductive wire or strip e. g. copper, concentrically arranged within a split cylindrical member 2 of conductive material, e. g. copper foil. The helix is wound over parallel insulating support rods 3 which carry at or near their ends further radial insulating rods 4 which in turn carry additional insulating rods 5 running parallel to the axis of the helix and also parallel to the rods 3 over which the said helix is wound. The outer insulating rods 5 serve 55 or,

to support the split foil cylinder 2 which is positioned within the said outer rods 5 and may be struck or otherwise afilxed thereto in any convenient manner. Since in this arrangement the supporting rods 3 for the helix are inside the turns thereof and the supporting rods ii for the foil are outside the same, the insulating material 0! which those rods are constituted will substantially not be cut by the field between the helix and foil, and accordingly dielectric losses will to a great extent be reduced. It will be appreciated that the middle point of the helix of a half wave coil construction in accordance with the preceding description will be a potential node and accordingly it may be directly connected to the split cylinder of foil.

Referring to Figs. 3 to 5, the inner conductor of the line is in the form of a helix l of flat strip conductor wound upon and stuck to an inner approximately cylindrical former 6 of paper or the like impregnated and coated with a suitable insulating varnish. The former 6 is somewhat longer than the helix and extends beyond it at both ends. The screen conductor 2 is of copper foil and is stuck to the inside of an approximately cylindrical backing I also of paper impregnated with a suitable varnish. The screen conductor is split with a plurality of splits 8 running parallel to the axis of the whole structure. adjacent splits starting from opposite edges and extending rather less than the length of the screen. The said screen conductor is made by slitting a sheet of copper foil as shown in Fig. 5 and then bending it up into a cylinder, the edges, which are at right angles to the slits forming the circular edges of the bent-up cylinder. The conductor 2 with its outer backing I is pushed over the inner conductor l and tormer i and is held in place by strips 9 of fairly still, insulation impregnated or coated paper. The ends of the conductor l are brought out parallel to the axis and are held firmly by insulation coated or impregnated paper layers Iii which pass over the conductor l and are also over the strips 8 and are stuck in position.

Figs. 6 and '7 are respectively a perspective view and an end view of a screen structure which may be substituted for that adopted in the coil structure shown in Figs. 3 to 5. In Figs. 6 and 7, the screen is in the form of a number of copper loll strips 2w stuck to the inside of an insulation impregnated or coated cylindrical backing I. The copper strips may be earthed at llib as shown in Fig. 6 by wires Ilia leading out to a common point, instead or using wires. the strips themselves.

may be extended beyond the backing and brought out to a common point in the same way as the wires we of Fig. 6, and may be connected to ground.

It will be observed that in all the illustrated coil structures the inner conductor is above its insulating support, the face of said conductor presented to the screen being free of insulating material and the outer conductor is inside its insuiating support. Thus, the field between outer and inner conductors does not pass through any insulating material (other than air)an important point for securing high efflciency in high frequency operation.

Quarter and half wave coil constructions in accordance with this invention and suitable for use in high frequency circuits can, if desired, be so arranged as to be variable for tuning purposes. For example, in the constructions of coil in accordance with this arrangement where there is an outer conductor or screen having a, slit running along its whole length, means may be provided for increasing and decreasing the width of the slit for tuning purposes; or an auxiliary slotted inner cylinder F (slotted so as not to act as a short circuiting turn) as shown in Figs. 1, 2 and 7, may be arranged to he slid coaxially to an adjustable extent into the coil proper of the coil construction; or a block or cylinder of ferromagnetic material may be arranged to he slid coaxially to an adjustable extent into the said coil proper; or an eddy current conductor may be arranged to be slid coaxially to an adjustable extent into the coil proper. Another way of providing for tuning in the case oi ahali wave length coil construction is to connect a variable condenser across the ends of the coil proper; or to connect a, variable condenser between one end of the coil proper and the outer conductor; or to connect variable condensers between each end of the coil proper and the outer conductor. Again, tuning may be provided for by so constructing the coil proper that it can be subjected to concertinalike control action, that is to say, so that its pitch may be varied substantially without altering its diameter or its concentric arrangement within the outer conductor.

What is claimed is:

In a variable high frequency inductance device, a conductive screen structure comprising a plurality of spaced conductive strips arranged to form a cage-like cylindrical member, a coil winding mounted within said screen and in coaxial relation therewith, the outer diameter of said coil winding being substantially smaller than the inner diameter of said screen whereby there is provided a substantial air space between the coil and the screen, a ferro-magnetic core for varying the inductance of said coil, said core being mounted for movement along itsaxis within said coil and in coaxial relation therewith, and a plurality of conductors, each having one end connected to a conductive strip of the screen and the other end connected to a common point, said conductors being arranged to form a cone-like structure, the apex of which is grounded.

NOEL MEYER RUST. 

